1. Field of the Invention
This invention relates to an improved apparatus for aerobic composting.
2. Discussion of the Prior Art
It is known to compost organic waste material, such as sludge from a waste water treatment facility, utilizing mechanical composting bins or vessels which circulate aeration air through the organic matter to be composted. The goal is to produce a non-malodorous organic material which can often be sold as a soil amendment or soil conditioner and which is at least not costly or objectionable to dispose of. The composting will also tend to reduce the amount of water in the organic matter, resulting in drying of the material to further alleviate disposal problems.
A commonly used approach to composting involves static or semi-static techniques in which the material to be composed is deposited in heaps or in pits or troughs in the surrounding terrain. Such approaches, are slow, require a considerable amount of land, may be environmentally dangerous and undesirable and tend to be uneconomical. To speed up the composting and to reduce size of the site required, various mechanical composting systems have been proposed.
One frequent approach to mechanical composting has involved the use of upright, cylindrical devices in the nature of silos, through which pressurized aeration air is circulated to aid in the decomposition process. Such vertical silos have certain disadvantages, such as excessive compaction of lower layers of material which have been vertically stacked as well as complicated internal mechanical equipment with high maintenance and downtime requirements due to the corrosive environment.
Horizontal composting methods and equipment have been proposed as alternatives to vertical composting silos. Horizontal composting has the advantage of a simple construction in which organic matter is moved horizontally along the length of the composting vessel in a stepwise fashion with the use of a hydraulically actuated ram. Each step consists of moving organic matter from the inlet against the entire mass of organic matter in the vessel, thereby moving the entire mass and discharging an amount of organic matter approximately equal to the amount of organic matter moved from the inlet into the composting chamber. The inlet is then again fed or charged with organic matter until full. Aeration air is circulated through the horizontal vessel to aid in carrying out the composting process in a relatively short period of time. Such a method and such an apparatus are disclosed in U.S. Pat. Nos. 4,384,877 and 4,436,817 to Nemetz, which U.S. Patents are hereby incorporated herein by reference.
Although horizontal composting has represented a substantial advance in the art, a greater flexibility in charging and discharging of the composter is desired. For example, it would be advantageous to accommodate charges of varying size and varying amounts of organic matter to be composted. Specifically, after a weekend during which composting has taken place, an amount of composted organic matter would be accumulated in the composting vessel which is larger than the normal weekday amount. The system described in the foregoing Nemetz patents can only charge and discharge an amount of organic matter which is approximately equal to the volume of the inlet or, more precisely, a space in the composting chamber representing a projection of the inlet opening into the composting Chamber. Thus, such a system affords no flexibility in charging and discharging.
Also, the method described by Nemetz requires the entire mass to be moved at every charging, thereby increasing energy costs. Further, each charging results in a discharge which requires manpower to monitor and to dispose of. Additionally, in the method and apparatus of the foregoing Nemetz patents, the density of the charge of organic matter is determined by the force required to compress the charge and move the entire mass.
A problem occurs in this known horizontal composting system where, as is often the case, material introduced into the composting chamber is relatively wet. Wet organic matter is heavy, thus requiring a large ram force in order to move the material. Force applied to the wet organic matter tends to be transmitted in all directions in a manner similar to that of a pressurized hydraulic fluid in a chamber. Force transmitted to the walls of the composting chamber in this way increases the frictional resistance of the wet charge to movement, causing the charge to bind in the chamber.
The problem compounds itself, because the large force on the ram applied to counter the resistance to movement compresses the organic matter further, making it heavier, more dense, and less porous, i.e. less able to permit the flow of aeration air through the organic matter. Air flow through the organic matter is essential for drying of the wet charge and for composting via aerobic decomposition. In the process of this aerobic decomposition, the moisture content of the material decreases, i.e. the material becomes dryer. It also becomes more porous, lighter, and easier to move through the composting vessel.
High moisture content in the material introduced into the composting vessel inhibits aerobic decomposition, inhibits air drying by circulation of air through the charge, increases the power demands and strength requirements of the equipment, increases the compaction of the organic matter and further inhibits the flow of air through the organic matter. In extreme cases, the high ram force required to move such highly compacted material through the vessel can cause equipment failures. In addition, the inhibition of air flow through the new charge of relatively wet organic matter requires increased pressures in the aeration air and increased pressure drops along the flow path of the aeration air. These pressure drops occur between air flowing into the composting chamber and air flowing out of the chamber after passing through the organic matter. The pressure drops necessitate increased aeration air pressures. Increased pressures, in turn, result in increased temperatures. With increased temperatures, the optimum temperature range for aerobic decomposition may be exceeded, thus further inhibiting the composting process.
Accordingly, it is an object of this invention to provide a system for composting organic matter which permits flexibility in the charging and discharging function.
It is a further object of the invention to better control the density, and thus the temperature, moisture content, and porosity of the mass of organic matter in the composter, particularly the density, temperature, moisture content and porosity of the new charge of organic matter in the critical first part of the composting vessel.
It is a further object of the present invention to provide a composting system in which excessive compaction of the organic matter in the composting chamber, particularly the critical first part of the composting chamber which receives the new charge, is avoided.
It is yet another object of the present invention to provide a composting system in which the density and porosity of the organic matter in the composting chamber, particularly the new charge of material in the first part of the composting chamber, may be controlled and maintained within an optimum range for composting a particular organic matter and for movement of the mass of organic matter through the composting vessel.
It is a further object of the present invention to provide a composting system in which the power requirements for the movement of the organic mass through the composter are reduced.
It is a related object of the present invention to provide a composting system in which the strength of the components of the composting apparatus may be less than of that of known systems.
It is a further object of the present invention to provide a composting system which ensures that aeration air may be circulated to an adequate extent through a new charge of relatively wet organic matter which has been introduced into a composting vessel.
It is still a further object of the present invention to provide a composting system which ensures that a new charge of relatively wet organic matter will not become excessively compacted as a result of its resistance to movement through the composting vessel.
It is another object of the present invention to provide a composting system in which the force required to move the entire mass of organic matter through the composting chamber will not have to be exerted through a new charge of relatively wet organic matter until that organic matter has been subject to air drying and initial aerobic decomposition to render the charge dryer, lighter, and more readily amenable to movement through the composting vessel.
It is yet another object of the present invention to provide a composting system in which the temperature of a new charge of relatively wet organic matter and the temperature of the aeration air circulating therethrough may be controlled by control of the extent of compaction of such new charge.
It is a further object of the present invention to provide a composting system in which the moisture content of a new charge of material in the composting chamber may be controlled by controlling the extent of compression of such organic matter by the ram.
It is a further object of the present invention to provide a composting system in which the extent of compaction of a new charge of material in the composting chamber is not governed by the amount of force required to move the entire mass of organic matter through the composting chamber.
It is yet another object of the present invention to provide a composting system in which the force exerted on the entire mass of organic matter in the composting chamber will be generally linearly and longitudinally transmitted through the entire mass to move the entire mass and in which such force will not be transmitted to a substantial extent to the walls of the chamber through a relatively wet new charge in the first part of the composting chamber.
It is a further object of the present invention to provide a composting system in which an existing mass of organic matter already in the composting chamber may be advanced toward the outlet opening of the composting vessel prior to any engagement of the existing mass of organic matter by a new charge of organic matter and in which new charges of organic matter are joined with the existing mass organic matter in operational steps which are carried out separately from such advancing of the entire mass.
It is a further object of the present invention to provide a composting system in which an evacuated space may be created in the composting chamber, which evacuated space is of substantially greater volume than the volume of an incremental inlet space, the incremental inlet space being defined by the projection of the inlet opening into the composting chamber.
It is yet another object of the present invention to provide a composting system in which the amount of discharged organic matter may be of substantially greater volume than the volume of the incremental inlet space.
It is a further object of the present invention to provide a composting system, which, while capable of providing an evacuated space and a discharge amount--both of which are of substantially greater volume than the volume of the incremental inlet space for handling relatively large amounts of organic matter--is not limited to handling such amounts and may provide for the creation of smaller spaces and smaller discharge amounts.
It is yet another object of the present invention to provide a composting system of the kind utilizing a ram for advancing organic material through the composting vessel in which it is not necessary to fully retract the ram in order to introduce a new charge of organic matter into the composting chamber of the vessel.
It is yet another object of the present invention to provide a composting system in which new charges of organic matter may be introduced into the composting vessels at various different positions in the composting chamber.
It is a further object of this invention to accomplish the above objects efficiently and inexpensively.
Other objects and advantages of this invention will become apparent from the specification and drawings which follow.